Gandalf started to believe that Bilbo Baggins' Magic Ring was the One. In T.A.3017 he visited Minas Tirith and studied the scroll. Isildur's description was vital in helping Gandalf identify the Ring. He visited Frodo Baggins in Bag End and testing his ring in the fireplace, confirmed it as the One Ring of Sauron.[1][2]

Gandalf visits Minas Tirith to discern the identity of Bilbo's Ring. A brief scene shows him guided to the vaults by a Gondorian keeper and reading the scroll, which is an elaborate prop in Tengwar calligraphy.